replacing clutch plates.
Time needed: If you're just replacing the plates, a couple of hours (less after you know where everything goes). We took everything off and inspected the parts for wear; if you do this step, count on adding another hour or so.
There's a detailed explanation of the drive train here, but to summarize: the outer housing (and therefore, the friction plates) spins with the crankshaft of the engine. When the clutch is disengaged (when the clutch lever is squeezed in), the plates don't touch one another. The outer housing and friction plates are spinning with the engine, but the inner housing and plain plates are stationary. When the clutch is engaged (the clutch lever is not squeezed in), a pressure plate at the outside of the clutch assembly pushes against the plates, forcing them to touch. The friction material on the friction plates "grabs" the plain plates, and forces them (and therefore, the inner housing) to spin with the friction plates and outer housing. The inner housing, incidentally, spins the main transmission gearshaft, which in turn, spins the countershaft, which turns the final drive (usually a chain) of the motorcycle.
You'll also want to start soaking the new friction plates in oil. Just pour some motor oil into a container, put the new friction plates in it, and pour some oil over them.
Once the crankcase cover is off, you've got a good view of the clutch assembly, the starter clutch, starter reduction gear, and the starter motor. If you're just replacing the plates, you don't need to worry about anything other than the clutch assembly. If you want to inspect the outer housing like the service manual suggests, you'll eventually have to remove the starter clutch assembly, too, so take a minute to look at everything and figure out what everything is.
A useful trick is to slide a penny in between the gears of the clutch assembly and the starter clutch. This is so that when you go at the clutch assembly bolts with your socket wrench, you don't accidentally turn the gears of the starter clutch. Don't use your family heirloom penny; when you're done with it, the coin will have seen better days.
OK, now on to actually replacing the clutch plates. :) The first thing to do with the clutch assembly is to remove the snap ring. You'll see some notches in the outermost plate on the clutch assembly (the pressure plate); stick your flathead screwdriver in a notch and use it to pry out the snap ring. Be careful, the ring is under a bunch of pressure and will likely attempt a violent escape. Don't have your head/eyes too close to the assembly when prying out the ring.
Once you've got the snap ring off, use the same notch-and-screwdriver trick to pry out the clutch lifter plate.
You can now see a large nut at the center of the assembly; this is the aptly-named clutch nut. Use the 27mm socket wrench to remove it. There'll be a washer behind it, don't lose that.
After the nut is off, you're going to start to disassemble the clutch spring assembly. These parts are what forces the plates together when the clutch is engaged, and what makes sure they're separate when the cluch is disengaged. One interesting thing is that the clutch spring isn't a spring as you'd normally think of one. It's a slightly concave ring of metal. There are two washers that fit behind it, causing a gap between the washers and the spring. This gap disappears when pressure is applied to the clutch spring.
At any rate, you're going to want to remove the clutch spring setting plate, clutch spring, and the two washers behind the clutch spring (the VF1000 only has one washer, but the VF750 has two).
The next piece to come off is the clutch pressure plate. This is the plate which literally applies pressure to the friction and plain plates to cause them to spin together. You can just pull that right off, and you'll see behind it the first friction plate and inner clutch housing.
After the pressure plate has been removed, you can just pull off all of the clutch plates. They'll just slide right out.
If all that you're doing is replacing plates, you can go ahead and put the new ones in. There is one more friction plate than plain plate, so the first plate that you put in should be a friction plate. You can skip to the reassembly section below, if you want.
If you're continuing on with us, after you remove the plates, there's a gear-looking thing left in the center of the assembly, around the shaft. For the VF750, this the one-way clutch assembly. Since the VF was originally a racebike, the purpose of this assembly is to prevent the rear wheel from locking up if the rider downshifts suddenly. It does this by disengaging half of the clutch plates when enough force is applied to the clutch mechanism as a whole (Trivia: the one-way clutch was first introduced in the '60s to the ROKON bike, so that the front wheel could travel faster then the rear wheel, but not vice-versa; apparently in racing, the front wheel needs to turn more quickly into a corner). . After you've removed it, you can hold the outer perimeter, and see how the inner part will turn in one direction, but not the other. Pretty neat.
After removing the one-way clutch assembly, go ahead and pull off the clutch inner housing. The clutch assembly looks pretty empty now.
Since we want to inspect the outer housing as well, we now have the fun job of removing the starter clutch and its buddies. First of all, you'll use a 17mm socket wrench to remove the bolt holding on the starter clutch. With the bolt off, it'll come right off. Make sure not to lose the washer that sits right behind the starter clutch. You can also then remove the starter reduction gear, which sits behind and to the right of the starter clutch.
Now you can remove the clutch outer housing. With the starter clutch out of the way, it'll slide right off. You can see the clutch springs on the backside of the outer housing.
My favorite part of doing this clutch replacement was seeing the innards of the crankcase after all of the clutch assembly had been removed. It's really cool. Here are a couple of pictures, one labelled. The shifter cam is pretty neat; it's star-shaped, so you can see by the little arm which gear the bike is in.
After all this cool stuff comes the long, boring, arduous task of inspecting all of everything that you just took off. I won't bore us both by listing it all; it's in your service manual, and suffice it to say that you're looking for burnt, scarred, or otherwise obviously flawed metal, warping, or metal shards flaking off. We found some of these metal splinters on the outer housing, so Peter took a metal file and carefully filed them off.
If you thought that was fun, you ain't seen nothing yet; next, we got to remove the old gasket from the crankcase cover. Sounds easy until you realize that the gasket was a 16-year-old paper/rubber mix gasket, which has since caked onto the metal cover. So out came the knife, and scraped did we. It sucked.
Now we get to put all this crap back together. The first thing to do is to find the four knobby pins on the primary gear. Turn the chain so that they're in the 12-o'clock, 3-o'clock, 6-o'clock, and 9-o'clock positions. Then, take a peek at the back of the outer clutch housing. There are four holes there; align these holes with the pins on the primary drive, and slide the outer housing back on. Use your flathead screwdriver to align the two sets of gears on the outer housing.
Next, you'll replace the inner clutch housing and then the one-way clutch. Nothing fancy to do here, just slide 'em on in. Once they're on, you'll notice that they have matching grooves; slide them around until these teeth/grooves are aligned with each other. It makes putting the plates on much easier.
Time to put the new plates on! Remember to start with a friction plate, and alternate between adding a friction plate and a plain plate. The VF750 has 7 friction plates and 6 plain plates. This will probably be different from your bike. Please make sure that you're using the correct amount of plates for your bike's make and model.
After all the plates are on (make sure a friction plate was the last one you inserted), slide on the clutch pressure plate.
Next, reinstall the clutch spring assembly. Hold the spring with the dished side up, like a bowl. Place the two washers on top of it, the larger one first, and then the smaller one. Then, take the clutch spring setting plate, and slide it through from the bottom. Install this entire assembly onto the crankshaft, with the dished side of the spring (the side with the washers) facing in.
Next, install the washer for the clutch nut, and replace the clutch nut. For the VF750, you'll want to torque the nut down to about 47 foot-pounds.
Once the clutch nut is torqued, replace the lifter plate and snap ring, and you're done with the clutch assembly. Remember to be careful when prying the snap ring back into place; it's really easy to pinch yourself.
Now, the only thing left to do is to re-install the starter clutch (assuming you removed it). I forgot to take pictures of this step, but it's really easy: first, align the punchmark on the gear shaft with the one on the starter clutch assembly. Slide the washer onto the shaft, and then replace the starter clutch (keeping the punchmarks aligned). Torque the starter clutch bolt to 70 foot-pounds. Finally, reinstall the starter reduction gear.
That's it! You're done! :)
Just for fun, here are two pictures which show the plates moving when the clutch is engaged/disengaged. The first picture shows the clutch plates when the clutch is engaged (all pressed together). The second picture shows the plates with the clutch disengaged (the lever squeezed in). You can see a gap between the plates, indicating that they aren't pressed together.